Ink-jet recording medium for dye- or pigment -based ink-jet inks

ABSTRACT

The present invention is drawn to a method of preparing a porous media substrate, comprising combining metal or semi-metal oxide particulates with a polymeric binder, wherein the metal or semi-metal oxide particulates are associated with at least one water soluble coating formulation additive. At least a portion of the water soluble coating formulation additive i) is in the form of unreacted additive, or ii) generates undesired electrolytes. Additional steps include removing at least a portion of the unreacted additive or undesired electrolytes, either before or after combining the metal or semi-metal oxide particulates with the polymeric binder, thereby forming a refined coating composition; and applying the refined coating composition to a media substrate to form an ink-receiving layer having a porous surface.

The present application is continuation-in-part application of U.S.patent application Ser. No. 10/854350, filed on May 26, 2004, theentirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to ink-jet printing. Moreparticularly, the present invention relates to the preparation ofsemi-metal or metal oxide-based media coatings for ink-jet applications.

BACKGROUND OF THE INVENTION

Ink-jet inks typically comprise an ink vehicle and a colorant, thelatter of which may be a dye or a pigment. Dye-based ink-jet inks usedin photographic image printing are almost always water-soluble dyes. Asa result, such dye-based ink-jet inks are usually not very water fast,i.e. images tend to shift in hue and edge sharpness is reduced uponexposure to humid conditions, especially when printed on mediasubstrates having a porous ink-receiving layer. In addition, imagescreated from these water-soluble dye-based ink-jet inks tend to fadeover time, such as when exposed to ambient light and/or air.Pigment-based inks on the other hand, allow the creation of images thatare vastly improved in humid fastness and image fade resistance. Pigmentbased images, however, are inferior to dye-based ink-jet inks withrespect to the desirable trait of color saturation and gloss uniformity.

Print media surfaces play a key role in fade properties, humid fastness,and the quality of ink-jet produced printed images. Thus, for a givenink, the degree of air fade, humid fastness, and image quality can bedependent on the chemistry of the media surface. As a result, manyink-jet inks can be made to perform better when an appropriate mediasurface is used. For example, pigment based ink can be very sensitive tomedia coating compositions. Images printed with pigment based ink onporous media usually exhibit haze, lower gloss, or even completely losegloss (also referred to as degloss) at high ink density. There are alsoproblems of air fade and humid fastness associated with dye-basedink-jet inks as well. The ability for a printed image to be handled andexhibit scratch resistance can also be poor if the media is notcompatible with ink-jet inks, particularly pigment-based ink-jet inks.

As such, it would be an advancement in the art to provide images thatexhibit high gloss and high gloss uniformity with both dye and pigmentbased ink. Without this degloss phenomena, the gloss uniformity can besignificantly improved in appearance. Also because of tight packing ofpigment colorants in pigment-based ink-jet inks, the scratch resistanceof the printed image can be enhanced. Still further, color gamut, blackdensity, and humid fastness for dye-based ink-jet inks can also besignificantly improved.

SUMMARY OF THE INVENTION

In accordance with embodiments of the present invention, various methodscan be used to provide coated media substrates that do not interactunfavorably with dye-based or pigment-based ink-jet inks. As such, amethod of preparing a porous media substrate can comprise various steps.One step includes combining metal or semi-metal oxide particulates witha polymeric binder, wherein the metal or semi-metal oxide particulatesare associated with at least one water soluble coating formulationadditive. At least a portion of the water soluble coating formulationadditive i) is in the form of unreacted additive, or ii) generatesundesired electrolytes. A further step includes removing at least aportion of the unreacted additive or undesired electrolytes, eitherbefore or after combining the metal or semi-metal oxide particulateswith the polymeric binder, thereby forming a refined coatingcomposition. The refined coating composition is then applied to a mediasubstrate to form an ink-receiving layer having a porous surface.

In an alternative embodiment, a media sheet can comprise a mediasubstrate and a refined coating composition applied to the mediasubstrate. The refined coating composition can include metal orsemi-metal oxide particulates, a polymeric binder, and at least onewater soluble coating formulation additive, wherein the water solublecoating formulation additive is present in the refined coatingcomposition in amount less than an initial amount. The initial amount ofthe water soluble coating formulation additive includes i) an amount ofunreacted additive or ii) generated undesired electrolytes. Thus, atleast a portion of the unreacted additive or undesired electrolytes areremoved from the initial amount prior to the refined coating compositionbeing applied to the media substrate.

Additional features and advantages of the invention will be apparentfrom the following detailed description which illustrates, by way ofexample, features of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Before particular embodiments of the present invention are disclosed anddescribed, it is to be understood that this invention is not limited tothe particular process and materials disclosed herein as such may varyto some degree. It is also to be understood that the terminology usedherein is used for the purpose of describing particular embodiments onlyand is not intended to be limiting, as the scope of the presentinvention will be defined only by the appended claims and equivalentsthereof.

In describing and claiming the present invention, the followingterminology will be used.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise. Thus, for example, reference to“a dye” includes reference to one or more of such materials.

“Image permanence” refers to characteristics of an ink-jet printed imagethat relate to the ability of the image to last over a period of time.Characteristics of image permanence include image fade resistance, waterfastness, humid fastness, light fastness, smudge resistance, airpollution induced fading resistance, scratch and rub resistance, etc.“Media substrate” or “substrate” includes any substrate that can becoated for use in the ink-jet printing arts including papers, overheadprojector plastics, coated papers, fabric, art papers, e.g., water colorpaper, and the like.

“Porous media coating” typically includes inorganic particulates, suchas silica or alumina particulates, bound together by a polymeric binder.Optionally, mordants and/or other additives can also be present. Suchadditives can be water soluble coating formulation additives includingmultivalent salts, such as aluminum chlorohydrate; organosilane reagentschemically attached or unattached to the inorganic particulates; and/oracidic components such as acidic crosslinking agents. An example of anacidic crosslinking agent that can be used to crosslink a polymericbinder, such as polyvinyl alcohol, is boric acid. The composition can beused as a coating for various media substrates, and can be applied byany of a number of methods known in the art. Additionally, suchcompositions can be applied in single layer or in multiple layers. Ifmultiple layers are applied, then these multiple layers can be of thesame or similar composition, or can be of different compositions.

The term “water soluble coating formulation additive” refers to ionicand/of other compositions that are added to coating compositions forpreparative, coating, or performance enhancing purposes. Though usefulfor these purposes, unreacted or excess amounts of such materials thatremain at resulting ink-receiving layers are undesirable with respect toprint quality. Additionally, such materials often generate electrolytesor salts as a byproduct that is also undesirable with respect to printquality. For example, excess water soluble coating formulation additivesor generated electrolytes/salts tend to coalesce or coagulate colorantsof ink-jet inks upon printing, as well diminish image gloss. Examples ofwater soluble coating formulation additives include unreacted acidiccrosslinking agents, unreacted or generated acids, unreacted orgenerated electrolytes/salts such as multivalent or high valent salts,and unreacted organosilane reagents. The removal of excess or generatedamounts of such materials in general can improve color gamut of printedimages, and particularly, the removal of salts can improve humidfastness. This removal process can occur prior to combining all of thecoating composition components together, or can occur after all of thecomponents are combined.

“Aluminum salt” refers to any of a number of salts, including aluminumchloride, aluminum chlorohydrate (ACH), Aluminum hydroxy sulfate,aluminum hydroxy nitrate, etc.

“Aluminum chlorohydrate,” “ACH,” “polyaluminum chloride,” “PAC,”“polyaluminum hydroxychloride,” or the like, refers to a class ofsoluble aluminum products in which aluminum chloride has been partlyreacted with a base. The relative amount of OH compared to the amount ofAl can determine the basicity of a particular product. The chemistry ofACH is often expressed in the form Al_(n)(OH)_(m)Cl(_(3n-m)), wherein ncan be from 1 to 50, and m can be from 1 to 150. Basicity can be definedby the term m/(3n) in that equation. ACH can be prepared by reactinghydrated alumina AlCl₃ with aluminum powder in a controlled condition.The exact composition depends upon the amount of aluminum powder usedand the reaction conditions. Typically, the reaction can be carried outto give a product with a basicity of 40% to 83%. ACH can be supplied asa solution, but can also be supplied as a solid.

There are other ways of referring to ACH, which are known in the art.Typically, ACH comprises many different molecular sizes andconfigurations in a single mixture. An exemplary stable ionic species inACH can have the formula [Al₁₂(OH)₂₄AlO₄(H₂O)₁₂]⁷⁺. Other examplesinclude [Al₆(OH)₁₅]³⁺, [Al₈(OH)₂₀]⁴⁺, [Al₁₃(OH)₃₄]⁵⁺, [Al₂₁(OH)₆₀]³⁺,etc. Other common names used to describe ACH or components that can bepresent in an ACH composition include Aluminum chloride hydroxide (8Cl);A 296; ACH 325; ACH 331; ACH 7-321; Aloxicoll; Aloxicoll LR; Aluminiumhydroxychloride; Aluminol ACH; Aluminum chlorhydrate; Aluminumchlorohydroxide; Aluminum chloride hydroxide oxide, basic; Aluminumchloride oxide; Aluminum chlorohydrate; Aluminum chlorohydrol; Aluminumchlorohydroxide; Aluminum hydroxide chloride; Aluminum hydroxychloride;Aluminum oxychloride; Aquarhone; Aquarhone 18; Astringen; Astringen 10;Banoltan White; Basic aluminum chloride; Basic aluminum chloride,hydrate; Berukotan AC-P; Cartafix LA; Cawood 5025; Chlorhydrol;Chlorhydrol Micro-Dry; Chlorhydrol Micro-Dry SUF; E 200; E 200(coagulant); Ekoflock 90; Ekoflock 91; GenPac 4370; Gilufloc 83;Hessidrex WT; HPB 5025; Hydral; Hydrofugal; Hyper Ion 1026; Hyperdrol;Kempac 10; Kempac 20; Kemwater PAX 14; Locron; Locron P; Locron S; Nalco8676; OCAL; Oulupac 180; PAC; PAC (salt); PAC 100W; PAC 250A; PAC 250AD;PAC 300M; PAC 70; Paho 2S; PALC; PAX; PAX 11S; PAX 16; PAX 18; PAX 19;PAX 60p; PAX-XL 1; PAX-XL 19; PAX-XL 60S; PAX-XL 61 S; PAX-XL 69; PAX-XL9; Phacsize; Phosphonorm; (14) Poly(aluminum hydroxy) chloride;Polyaluminum chloride; Prodefloc AC 190; Prodefloc AL; Prodefloc SAB 18;Prodefloc SAB 18/5; Prodefloc SAB 19; Purachem WT; Reach 101; Reach 301;Reach 501; Sulzfloc JG; Sulzfloc JG 15; Sulzfloc JG 19; Sulzfloc JG 30;TAI-PAC; Taipac; Takibine; Takibine 3000; Tanwhite; TR 50; TR 50(inorganic compound); UPAX 20; Vikram PAC-AC 100S; WAC; WAC 2; Westchlor200; Wickenol 303; Wickenol CPS 325 Aluminum chlorohydrate Al₂ClH₅O₅ orAl₂(OH)₅Cl.2H₂O or [Al(OH)₂Cl]_(x) or Al₆(OH)₁₅Cl₃; Al₂(OH)₅Cl]_(x)Aluminum chlorohydroxide; Aluminum hydroxychloride; Aluminum chloride,basic; Aluminum chloride hydroxide; [Al₂(OH)_(n)Cl_(6-n)]_(m);[Al(OH)₃]_(n)AlCl₃; or Al_(n)(OH)_(m)Cl(_(3n-m)) (where generally,0<m<3n); for example. In one embodiment, preferred compositions includealuminum chlorides and aluminum nitrates of the formula Al(OH)₂X toAl₃(OH)₈X, where X is Cl or NO₃. In another embodiment, preferredcompositions can be prepared by contacting silica particles with analuminum chlorohydrate (Al₂(OH)₅Cl or Al₂(OH)Cl_(5.n)H₂O). It isbelieved that contacting a silica particle with an aluminum compound asdescribed above causes the aluminum compound to become associated withor bind to the surface of the silica particles. This can be either bycovalent association or through an electrostatic interaction to form acationic charged silica, which can be measured by a Zeta potentialinstrument.

“Organosilane reagent” or “reagent” includes compositions that comprisea functional or active moiety which is covalently attached to a silanegrouping. The organosilane reagent can become covalently attached orotherwise attracted to the surface of metal or semi-metal oxideparticulates, such as silica or alumina. Examples of moieties that canprovide a desirable function include anionic dye anchoring groups (suchas amines, quaternary ammonium salts, etc.), ultraviolet absorbers,metal chelators, hindered amine light stabilizers, reducing agents,hydrophobic groups, ionic groups, buffering groups, or functionalitiesfor subsequent reactions. The functional moiety portion of theorganosilane reagent can be directly attached to the silane grouping, orcan be appropriately spaced from the silane grouping, such as by from 1to 10 carbon atoms or other known spacer groupings. The silane groupingof the organosilane reagent can be attached to inorganic particulates ofthe porous media coating composition through hydroxyl groups, halogroups, or alkoxy groups present on the reagent. Alternatively, in someinstances, the organosilane reagent can be merely attracted to thesurface of the inorganic particulates.

The term “ink-receiving layer(s)” refers to a layer or multiple coatinglayers that are applied to a media substrate, and which are configuredto receive ink upon printing. As such, the ink-receiving layer(s) do notnecessarily have to be the outermost layer, but can be a layer that isbeneath another coating.

The term “about” when referring to a numerical value or range isintended to encompass the values resulting from experimental error thatcan occur when taking measurements.

Ratios, concentrations, amounts, and other numerical data may bepresented herein in a range format. It is to be understood that suchrange format is used merely for convenience and brevity and should beinterpreted flexibly to include not only the numerical values explicitlyrecited as the limits of the range, but also to include all theindividual numerical values or sub-ranges encompassed within that rangeas if each numerical value and sub-range is explicitly recited. Forexample, a weight range of about 1 wt % to about 20 wt % should beinterpreted to include not only the explicitly recited concentrationlimits of 1 wt % to about 20 wt %, but also to include individualconcentrations such as 2 wt %, 3 wt %, 4 wt %, and sub-ranges such as 5wt % to 15 wt %, 10 wt % to 20 wt %, etc.

With this in mind, the present invention is drawn to a method ofpreparing a porous media substrate can comprise various steps. One stepincludes combining metal or semi-metal oxide particulates with apolymeric binder, wherein the metal or semi-metal oxide particulates areassociated with at least one water soluble coating formulation additive.At least a portion of the water soluble coating formulation additive i)is in the form of unreacted additive, or ii) generates undesiredelectrolytes. A further step includes removing at least a portion of theunreacted additive or undesired electrolytes, either before or aftercombining the metal or semi-metal oxide particulates with the polymericbinder, thereby forming a refined coating composition. The refinedcoating composition is then applied to a media substrate to form anink-receiving layer having a porous surface.

In an alternative embodiment, a media sheet can comprise a mediasubstrate and a refined coating composition applied to the mediasubstrate. The refined coating composition can include metal orsemi-metal oxide particulates, a polymeric binder, and at least onewater soluble coating formulation additive, wherein the water solublecoating formulation additive is present in the refined coatingcomposition in amount less than an initial amount. The initial amount ofthe water soluble coating formulation additive includes i) an amount ofunreacted additive or ii) generated undesired electrolytes. Thus, atleast a portion of the unreacted additive or undesired electrolytes areremoved from the initial amount prior to the refined coating compositionbeing applied to the media substrate.

As discussed, images produced using either pigment-based ink-jet inks ordye-based ink-jet inks can be affected by the print media to which theink is applied. In particular, pigment-based inks, which sometimescontain latex particulates and/or binders, can be very sensitive toundesired material that are often present in ink-receiving layers ofprint media. For example, water soluble coating formulation additives,such as acids, multivalent ions, or aluminum chlorohydrate, can bedesired for the manufacture certain media coatings. However, thesematerials in excess, after the coating composition has dried to form anink-receiving layer, can have undesired an affect on the ink-jet ink.Further, these and other similar materials, when added, can generateunwanted electrolytes or salts. For example, a coating compositionprepared that includes semi-metal oxide or metal oxide particulates,polyvinyl alcohol, sodium borate, sodium hydroxide, and aluminumchlorohydrate results in unwanted sodium chloride salts. These and otherionic compositions can cause pigment coagulation to occur, resulting ina reduction or loss in gloss. In some cases, scratch resistance canbecome poor due to pigment interaction with such media surfaces.Additionally, unreacted boric acid, which is often used as acrosslinking agent to increase the binding strength of polyvinyl alcoholbinder in semi-metal or metal oxide-based media coatings, can also beproblematic in finished ink-receiving layers. Alternatively, withdye-based ink-jet inks, unreacted or excess water soluble coatingformulation additives can reduce color chroma and black density, as wellas reduce image gloss.

In accordance with this recognized problem, the present invention isdrawn to specialty ink-jet media and methods of making the same, whereingenerated, excess, or unreacted amounts of these ionic and/or otherinterfering water soluble components are at least partially removed toproduce improved compatibility with ink-jet ink components, such as dyesand/or pigments. Printed images on such media have shown uniform andhigh gloss, as well as improved scratch resistance with pigment-basedink-jet inks.

In accordance with embodiments of the present invention, various methodscan be used to provide coated media substrates that do not interactunfavorably with dye-based or pigment-based ink-jet inks. In some of theembodiments described herein, a water soluble coating formulationadditive is typically included in a coating composition for improving atleast one of a coating preparation property, a coating applicationproperty, or a media performance property. However, unreactedadditive(s) or additive(s) that generate undesired electrolytes or saltscan create printing difficulties, as previously set forth. There are atleast two basic strategies of removing unreacted additive(s) orgenerated electrolytes or salts, including removing theadditive(s)/generated electrolytes prior to application of a coatingcomposition, or after application of a coating composition, i.e. afterforming the ink-receiving layer. In accordance with the presentinvention, these unreacted additive(s) or generated electrolytes orsalts are removed prior to application of the coating composition.

Turning to specific media coating components, with more specificreference to the semi-metal or metal oxide particulates, suchparticulates that can be selected for use include silica, alumina,titania, zirconia, aluminum silicate, calcium carbonate, and/or othernaturally occurring pigments.. These compositions can be in variousforms and in various shapes; for example, silica can be fumed silica,colloidal silica, precipitated silica, or grounded silica gel, dependingon the affect that is desired to achieve. In one embodiment, 30 nm to100 nm spherical silica particulates can be used to provide a glossyappearance, whereas larger less spherical particulates can provide aless glossy appearance. More irregular shapes, on the other hand, canprovide more voids between particles than may be present with tightlypacked spherical particulates.

As the semi-metal or metal oxide particulates are not self-adherent,typically, a binder is added to the composition to bind the particulatestogether. An amount of binder is typically added that provides a balancebetween binding strength and maintaining particulate surface voids andinter-particle spaces for allowing ink to be received. Exemplary bindersthat can be used include polyvinyl alcohol, both fully hydrolyzed andpartially hydrolyzed, such as Airvol supplied by Air Product or Mowiolsupplied by Clariant; modified polyvinyl alcohol, such asacetoacetylated polyvinyl alcohols commercially available as theGOHSEFIMER Z series from Nippon Gohsei; amine modified polyvinylalcohol; and polyvinyl alcohol modified by silane coupling agent. Otherbinders that can be used include polyester, polyester-melanine,styrene-acrylic acid copolymers, styrene-acrylic acid-alkyl acrylatecopolymers, styrene-maleic acid copolymers, styrene-maleic acid-alkylacrylate copolymers, styrene-methacrylic acid copolymers,styrene-methacrylic acid-alkyl acrylate copolymers, styrene-maleic halfester copolymers, vinyl naphthalene-acrylic acid copolymers, vinylnaphthalene-maleic acid copolymers, and salts thereof. In someembodiments, it can be more desirable to use polyvinyl alcohol and/ormodified polyvinyl alcohol as the interaction between the binder andsilica is very strong, resulting in a formed coating that issubstantially water insoluble.

To improve the binding strength of the binder, a crosslinking agent,such as boric acid, can be added to the coating composition. Forexample, by adding boric acid to a system including polyvinyl alcohol, acrosslinking reaction can be carried out with the binder, which providesfor improved binding strength. Improved binding strength can lead toreduced cracking at the ink-receiving layer. When a crosslinking agentis used, less binder may be required for use.

Other crosslinking agents that can be used include borate salt, titaniumsalt, vanadium and chromium salts, melamine formaldehyde, glyoxal,thiourea formaldehyde, and Curesan. Though a purpose of the invention isto remove unreacted water soluble coating formulation additives, thisdoes not mean that only water soluble coating formulation additive mustbe used, as other formulation additives that do not interfere with printquality can also be used therewith.

In accordance with the above embodiments, the semi-metal oxide or metaloxide particulates can be admixed or treated with multivalent salt(s).Exemplary salts that can be added to coating compositions to providebenefit to the coating composition, but which should be removed from thecoating composition if excess amounts are present include aluminumsalts, such as aluminum chlorohydrate, and trivalent or tetravalentmetal oxides with metals such as aluminum, chromium, gallium, titanium,and zirconium. Alternatively, if such multivalent salt(s) generateunwanted or interfering electrolytes, those electrolytes canalternatively or additionally be removed. In one embodiment, if aluminumchlorohydrate is used, it can be present in the coating composition atfrom 2 wt % to 20 wt % compared to the silica content, and in a moredetailed embodiment, the aluminum chlorohydrate can be present at from 5wt % to 10 wt %.

In addition to the salt groups that can be added, the semi-metal ormetal oxide particulates can also be modified with organic groups.Specifically, organosilane reagents can be added to thesurface-activated silica to add additional positively charged moietiesto the surface, or to provide another desired function at or near thesurface, e.g., ultraviolet absorber, chelating agent, hindered aminelight stabilizer, reducing agent, hydrophobic group, ionic group,buffering group, or functionality for a subsequent reaction. As thesereagents are primarily organic, they can provide different propertieswith respect to ink-jet ink receiving properties.

In one embodiment, the organosilane reagents can be amine-containingsilanes. In a more detailed embodiment, the amine-containing silanes caninclude quaternary ammonium salts. Examples of amine-containing silanesinclude 3-aminopropyltrimethoxysilane,N-(2-aminoethyl-3-aminopropyltrimethoxysilane,3-(triethoxysilylpropyl)-diethylenetriamine,poly(ethyleneimine)trimethoxysilane, aminoethylaminopropyltrimethoxysilane, aminoethylaminoethylaminopropyl trimethoxysilane, andthe quaternary ammonium salts of the amine coupling agents mentionedabove. An example of a quaternary ammonium salt organosilane reagentincludes trimethoxysilylpropyl-N, N, N-trimethylammonium chloride.

Alternatively, other organosilane coupling agents can be useful for themodification of a silica surface, includingbis(2-hydroethyl)-3-aminopropyltriethoxysilane,3-mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane,bis(triethoxysilylpropyl)disulfide, 3-aminopropyltriethoxysilane,3-aminopropylsilsesquioxane, bis-(trimethoxysilylpropyl)amine,N-phenyl-3-aminopropyltrimethoxysilane,N-aminoethyl-3-aminopropylmethyidimethoxysilane,3-ureidopropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane,N-(trimethyloxysilylpropyl)isothiouronium chloride,N-(triethoxysilpropyl)-O-polyethyleneoxide,3-(triethoxylsilyl)propylsuccinic anhydride, 3-(2-imidazolin-1-yl)propyltriethoxysilane, and reagents sold under the trade name SILQUEST(OSI Products), SiventoSilane (Degussa), Dynasylan, and/or Cab-O-Sil M-5(Cabot Corp.).

Other organosilane reagents can also be used that provide a benefit to aprinting system, such as reagents that include an active ligand ormoiety. Examples of such active ligands or moieties include those thatact as an ultraviolet absorber, chelating agent, hindered amine lightstabilizer, reducing agent, hydrophobic group, ionic group, bufferinggroup, or functionality for a subsequent reaction. To illustrate this,Formula 1 provides examples of organosilane reagents that canaccordingly be used:

In Formula 1 above, from 0 to 2 of the R groups can be H, —CH₃, —CH₂CH₃,or —CH₂CH₂CH₃; from 1 to 3 of the R groups can be halide or alkoxy; andfrom 1 to 3 of the R groups can be an active or functional moiety, suchas one described previously. If a halide is present, then Formula 1 canbe said to be an organohalosilane reagent. If alkoxy is present, thenFormula 1 can be said to be an organoalkoxysilane reagent.

An inclusive list of functional moieties that can be attached to themetal or semi-metal oxide surface includes straight or branched alkylhaving from 1 to 22 carbon atoms, cyano, amino, halogen substitutedamino, carboxy, halogen substituted carboxy, sulfonate, halogensubstituted sulfonate, halogen, epoxy, furfuryl, mercapto, hydroxyl,pyridyl, imidazoline derivative-substituted lower alkyl, lowercycloalkyl, lower alkyl derivatives of cycloalkyl, lower cycloalkenyl,lower alkyl derivatives of cycloalkenyl, lower epoxycycloalkyl, loweralkyl derivatives of epoxycycloalkyl, phenyl, alkyl derivatized phenyl,phenoxy, poly(ethylene oxides), poly(propylene oxide), copolymer ofpolyethyleneoxide and poly(propyleneoxide), vinyl, benzylic halogen,alkyl derivatized phenoxy, quaternary amine, monoethyleneimine, orpolyethyleneimine.

In practice, adding a multivalent salt, such as aluminum chloridehydrate, can provide stability to the coating mix prior to application,and reduces the tendency for the receiving layer to be low in gloss.Additionally, as mentioned, boric acid can be added to improve thebinding power of the coating composition, thereby reducing the tendencyof a dried receiving layer to crack. As described, though the aluminumchlorohydrate and the boric acid provide these benefits, they can alsohave the negative affect of causing ink-jet inks under perform ifpresent in excess amounts, or if the electrolytes formed therefromremain in the coating composition or the ink-receiving layer of theresulting print media. For example, pigment-based inks, in the presenceof boric acid and aluminum chlorohydrate (or their resulting electrolytereaction products) on a media substrate, have a tendency to lose theirgloss at a higher ink load. Thus, gloss uniformity can suffer. In otherwords, unreacted or generated high valent salts and acid can work toundesirably coagulate ink. When dye- or pigment-based inks coagulate,color gamut suffers and image scratch resistance will deteriorate. Byremoving at least a portion of excess or unreacted amounts of suchadditive(s) from the coating composition, or by removing electrolytes orsalts generated from the additives, prior to forming the ink-receivinglayer on the media substrate, the benefits of using the additive(s) canbe realized, and at the same time, many of the negatives resulting fromthe presence of residual, excess, or unreacted amounts of suchadditive(s) that would otherwise remain present in the coatingcomposition can be minimized. Thus, by substantially removing excessacid and excess high valent salts from the coating composition orresulting ink-receiving layer, image quality can be greatly improved.

Regarding removing unwanted additives or generated electrolytes from thecoating composition or resulting ink-receiving layer, in accordance withembodiments of the present invention, such removal can occur prior toapplication of the coating composition. Removal of the unwanted excessadditives or generated material prior to application of the coating canbe by one of a number of methods, including ultrafiltration, dialysis,ion-exchange, reverse osmosis, and combinations of these processes. Byway of example, without being bound by any particular removal method,the process of ultrafiltration is exemplified herein.

Ultrafiltration is a membrane filtration technology that can be used toseparate small colloids and large molecules from liquids (such as water)and small molecules. A back pressure can be applied at, for example, 100psi. Thus, a subject composition is forced against a semi-permeablemembrane that allows water molecules and other small molecules to pass,while maintaining larger molecules, such as colloids. Deionized water isadded as water is being removed through the membrane wash the colloidsand replenish the water content. Typically, the process ofultrafiltration is used for removing particles from a composition atfrom about 2 nm to about 100 nm, i.e. a process defined as betweenreverse osmosis and microfiltration. For example, a filter size of about50 nm or less can remove or lose generated or unreacted electrolytes(about 10 nm), and can keep everything greater than about 70 nm.Typically, with ultrafiltration, organics or colloids over 1,000 MW areretained while passing ions and smaller colloids or organics. Similarly,diafiltration can be used to remove the low molecular weight watersoluble species, such as salts or electrolytes, from the solution ordispersion.

The membranes used for both ultra and diafiltration typically have amolecular weight cutoff (MWCO) ranging from 100 to 500,000 Daltons suchthat species smaller than the rated MWCO of the membrane are capable ofpassing through the membrane. Further, these membranes also usually havetwo layers, e.g., a thin (0.1 to 0.5 μm), semi-permeable membrane madefrom cellulose ester or polyethersulfone and a substructure supportmaterial. During manufacturing, the membranes can be cast onto themembrane support. Only the layer of semi-permeable membrane comes incontact with the sample during ultrafiltration or diafiltration. Thesupport material below the membrane does not typically affect thefiltration characteristics of the membrane.

In conventional ultrafiltration/microfiltration configurations, aprocess solution is pressurized, typically at from 10 psi to 70 psi,while in contact with a supported semi-permeable membrane is maintained.Solutes smaller than the MWCO emerge as ultrafiltrate, and the retainedmolecules are concentrated on the pressurized side of the membrane.Pressure sources such as compressed gas (nitrogen) and peristaltic pumpsystems are commonly used.

With diafiltration, the target small molecule flows through a membranein convective flow. The volume of permeate is continuously added to thefeed as solvent. The efficiency of removal can be very high, but theproperties of the membrane and the process conditions should be chosencarefully.

Still another method of removing low molecular weight electrolytes fromaqueous solution or dispersion is dialysis. Dialysis defuses smallmolecules through a permeable selective membrane that will not allowpassage by diffusion of the other constituents of the feed. Theconcentration of the target molecule in the feed decreases with time.Thus, the efficiency of removal is also decreased and usually takes alonger time to achieve separation results.

In an exemplary embodiment in accordance with the present inventioninvolving removal of excess additive(s) or generated electrolytes priorthe application of a coating composition, a media coating can beprepared that exhibits improved light fastness, scratch resistance, andimage quality. Such a coating can include a porous pigment, such asfumed silica (about 50 wt % to 85 wt %), as a primary structuralparticulate component; a multivalent salt, such as aluminumchlorohydrate (about 5 wt % to 8 wt %), which provides a cationicsurface charge to the system; and a binder, such as polyvinyl alcohol(about 15 wt % to 20 wt %) to bind the silica and the aluminumchlorohydrate together. To increase the binding power of the polyvinylalcohol, a crosslinking agent, such as boric acid (about 0.5 wt % to 5wt %) can be added. The coating mix can be refined by removing excessamounts of the aluminum chlorohydrate by ultrafiltration, for example.Alternatively, aluminum chlorohydrate-treated silica can be treated byultrafiltration prior to combining with the polyvinyl alcohol and/orcrosslinking agent. In one example, ultrafiltration can be carried outusing a porous membrane having an average pore size of about 50 nm. Inanother example, back pressure of about 100 psi can be applied to thecomposition, and small substances, including undesired electrolytesand/or unreacted additive, will pass through the pores along with thewater. As such material is passed through the pores, deionized water canbe used to replenish the lost water, thereby refining the coatingcomposition. The coating mix in a more refined state can then be appliedon a non-absorbing base or substrate, and subsequently dried. The coatweight can be controlled at from 15 g/m² to 35 g/m². In one embodiment,a second coating including more spherical colloidal silica (40 nm to 100nm) can be applied as an overcoat to provide a glossy and scratchresistant finish. If the second coating is not formulated with ioniccompositions or acid, for example, a refining or removing step is notnecessary, though such a step is not precluded.

Distinct from removing unwanted additives and/or generated electrolytesprior to coating, a post coating washing step can additionally becarried out. In other words, washing can be carried out after theink-receiving layer has been formed. Such a washing step can be carriedout by bathing, spraying, or by other known washing techniques.Typically, the water can be at about room temperature, thoughtemperatures from about 0° C. to 90° C. can be used. In one embodiment,hot water from 30° C. to 50° C. can be used. The water used can bedeionized water, hard water, soft water, or water with additives. Forexample, the water can include a buffer (0.1 to 1% solids) to controlthe pH during the washing stage at from pH 5 to 7.5. It has beendiscovered that washing with low concentration buffer is good forpigment based ink gloss improvement, and only has a slight negativeeffect on humid bleed. That is because of that most of buffer compoundsare low molecular acids and salts. Not every salt can interact withpigment colorant to decrease gloss, but typically, salts deterioratehumid bleed. Whatever water type (with or without additives) is used,the washing step can be used to contribute to the final pH of the mediasheet. In one embodiment, the pH of an ink-receiving layer of the mediasheet can be from about pH 4 to about pH 7.5. In another embodiment, thepH of the ink-receiving layer can be from about pH 5 to about pH 6.Other additives that can be present in the water include additives thatcontribute to print quality, such as air fade additives or the like.Examples of air fade additives that can be included are radicalscavengers, hindered amines, and/or thio compounds such asthiodiethylene glycol.

The media substrate that can be used can be of any substrate known inthe art, and can include papers, overhead projector plastics, coatedpapers, fabric, art papers, e.g., water color paper, photobase, or thelike. The application of the porous coating composition to a mediasubstrate can be by any method known in the art, such as air knifecoating, blade coating, gate roll coating, doctor blade coating, Meyerrod coating, roller coating, reverse roller coating, gravure coating,brush coating, sprayer coating, or cascade coating.

Ink-jet ink compositions that can be used to print on the coated mediacompositions of the present invention are typically prepared in anaqueous formulation or liquid vehicle which can include water,co-solvents, surfactants, buffering agents, biocides, sequesteringagents, viscosity modifiers, humectants, binders, and/or other knownadditives. Colorants, such as dyes and/or pigments are also present toprovide color to the ink-jet ink. In one aspect of the presentinvention, the liquid vehicle can comprise from about 70 wt % to about99.9 wt % of the ink-jet ink composition. In another aspect, other thanthe colorant, liquid vehicle can also carry polymeric binders, latexparticulates, and/or other solids.

EXAMPLES

The following examples illustrate the embodiments of the invention thatare presently best known. However, it is to be understood that thefollowing are only exemplary or illustrative of the application of theprinciples of the present invention. Numerous modifications andalternative compositions, methods, and systems may be devised by thoseskilled in the art without departing from the spirit and scope of thepresent invention. The appended claims are intended to cover suchmodifications and arrangements. Thus, while the present invention hasbeen described above with particularity, the following examples providefurther detail in connection with what are presently deemed to be themost practical and preferred embodiments of the invention.

Example 1 Preparation of ACH-Treated Silica

To 375 ml of water were added 11 mL of 2N NaOH and 27.9 grams of 50%aluminum chlorohydrate (ACH) under strong agitation. Then, 86.1 grams offumed silica Cab-o-sil M-5 was added into the dispersion. The productwas aged for about 24 hours producing a cationic silica sol having 20 wt% solids. In this embodiment, the aluminum chlorohydrate was used asdispersing agent which converted the silica surface from anionic tocationic, providing a repulsion force with respect to the silicapigments, thereby preventing the sol from flocculating and providingacceptable stability.

Example 2 Refining ACH-Treated Silica Prior to Coating on MediaSubstrate

An ACH treated silica is prepared by the method described in Example 1.The final wt % of solids is adjusted to about 20%, and the pH of thesilica is adjusted to about 3.0. A Vivaflow 200 (by Vivascience,Germany) tangential flow (or cross flow) diafiltration module is used toremove the electrolytes from the silica dispersion. About one liter ofthe 20% ACH treated silica is then charged to a two liter Erlenmeyerflask, and the flask was immersed to a constant temperature bath at 50°C. The diafiltration is carried out using a 50,000 MWCO polyethersulfonemembrane, and a Cole-Parmer peristatic pump-head accepting size 15tubing and a pressure gauge are attached. The heated silica dispersionis pumped through the membrane and the back pressure is controlled atfrom 20 psi to 30 psi. To maintain a constant volume and constant solidof the fluid, a reservoir containing deionized water is connected to thesystem. As water/salt passes through the membrane, the vacuum that iscreated in the sample reservoir draws deionized water in exchangethrough the feed tubing from the feed reservoir. The conductivity of thewaste aqueous solution is monitored continuously. This process iscontinued until the conductivity of the waste solution is reduced towithin 5 times of the deionized water. In general, this is accomplishedwith an exchange volume of approximately 5 times of the original samplevolume. The cleaned silica dispersion is recovered and cooled to roomtemperature. Alternatively, reduction is conductivity can be measuredbased on a decrease in the original conductivity of the coating solutionto 20%. Once the cleaned silica dispersion is formed, it can be admixedwith a binder composition and coated on a media substrate. By followingthis process, the conductivity of the particles in the coatingcomposition can be reduced anywhere from about 25% to 75%, which issignificant with respect to ink or dye interaction with these coatings.

While the invention has been described with reference to certainpreferred embodiments, those skilled in the art will appreciate thatvarious modifications, changes, omissions, and substitutions can be madewithout departing from the spirit of the invention. It is thereforeintended that the invention be limited only by the scope of the appendedclaims.

1. A method of preparing a porous media substrate, comprising: combiningmetal or semi-metal oxide particulates with a polymeric binder, whereinthe metal or semi-metal oxide particulates are associated with at leastone water soluble coating formulation additive, wherein at least aportion of the water soluble coating formulation additive i) is in theform of unreacted additive, or ii) generates undesired electrolytes;removing at least a portion of the unreacted additive or undesiredelectrolytes, either before or after combining the metal or semi-metaloxide particulates with the polymeric binder, thereby forming a refinedcoating composition; and applying the refined coating composition to amedia substrate to form an ink-receiving layer having a porous surface.2. A method as in claim 1, wherein metal or semi-metal oxide is silica.3. A method as in claim 1, wherein metal or semi-metal oxide is alumina.4. A method as in claim 1, wherein the binder includes a member selectedfrom the group consisting of polyvinyl alcohol, modified polyvinylalcohol, and combinations thereof.
 5. A method as in claim 1, whereinwater soluble coating formulation additive includes a member selectedfrom the group consisting of ionic mordants, ionic multivalent ions,ionic organosilane reagents, acidic components, crosslinking agents,organic salts, inorganic salts, and combinations thereof.
 6. A method asin claim 5, wherein the water soluble coating formulation additiveincludes an ionic multivalent ion, said ionic multivalent ion includingaluminum chlorohydrate.
 7. A method as in claim 5, wherein the watersoluble coating formulation additive includes an ionic organosilanereagent, said ionic organosilane reagent including an amine moiety.
 8. Amethod as in claim 5, wherein the water soluble coating formulationadditive includes an acidic component, said acidic component includingan acidic crosslinking agent.
 9. A method as in claim 8, wherein theacidic crosslinking agent is boric acid.
 10. A method as in claim 1,wherein the refined coating composition further includes an air fadeadditive configured to improve air fade resistance of an image printedon the porous media substrate.
 11. A method as in claim 10, wherein theair fade additive is selected from the group consisting of hinderedamines, thio compounds, and combinations thereof.
 12. A method as inclaim 1, wherein the step of removing is by a process selected from thegroup consisting of ultrafiltration, dialysis, ion exchange, reverseosmosis, and combination of process thereof.
 13. A method as in claim12, wherein the step of removing is by ultrafiltration.
 14. A method asin claim 13, wherein the ultrafiltration is carried out using a porousfilter having an average pore size from 20 nm to 100 nm.
 15. A method asin claim 1, wherein the porous surface has a pH from about 4 to about7.5.
 16. A method as in claim 15, wherein the porous surface has a pHfrom about 5 to about
 6. 17. A method as in claim 1, wherein the step ofremoving occurs prior to combining the metal or semi-metal oxideparticulates with the polymeric binder.
 18. A method as in claim 1,wherein, after the applying step, the porous surface is subsequentlycoated with a second coating that is substantially devoid water solublecoating formulation additive.
 19. A method as in claim 1, wherein themedia substrate includes an inorganic porous media precoat, and whereinthe step of applying the refined coating composition to the mediasubstrate is by overcoating the precoat.
 20. A method as in claim 1,further comprising the step of washing the ink-receiving layer.
 21. Amethod as in claim 1, wherein the washing step is to remove additionalunreacted additive or undesired electrolytes.
 22. A media sheet,comprising: a media substrate; a refined coating composition applied tothe media substrate, said refined coating composition including metal orsemi-metal oxide particulates, a polymeric binder, and at least onewater soluble coating formulation additive, wherein the water solublecoating formulation additive is present in the refined coatingcomposition in amount less than an initial amount, said initial amountof the water soluble coating formulation additive including i) an amountof unreacted additive, or ii) generated undesired electrolytes, at leasta portion of said unreacted additive or undesired electrolytes beingremoved from the initial amount prior to the refined coating compositionbeing applied to the media substrate.
 23. A media sheet as in claim 22,wherein the media substrate is selected from the group consisting ofpaper, overhead projector plastic, coated paper, fabric, art paper,water color paper, and photobase.
 24. A media sheet as in claim 22,wherein the property that is enhanced is gloss uniformity upon printingink on the media sheet.
 25. A media sheet as in claim 22, wherein theproperty that is enhanced is color gamut upon printing ink on the mediasheet.
 26. A media sheet as in claim 22, wherein the property that isenhanced is humid bleed reduction upon printing ink on the media sheet.27. A media sheet as in claim 22, wherein the property that is enhancedis reduced coating composition cracking upon application to the mediasubstrate and drying.
 28. A media sheet as in claim 22, wherein theproperty that is enhanced is ink-receiving capacity upon printing ink onthe media sheet.
 29. A media sheet as in claim 22, wherein metal orsemi-metal oxide is selected from the group consisting of silica,alumina, titania, zirconia, and combinations thereof.
 30. A media sheetas in claim 22, wherein the binder includes a member selected from thegroup consisting of polyvinyl alcohol, modified polyvinyl alcohol, andcombinations thereof.
 31. A media sheet as in claim 22, wherein thewater soluble coating formulation additive includes a member selectedfrom the group consisting of ionic mordants, ionic multivalent ions,ionic organosilane reagents, acidic components, organic salts, inorganicsalts, and combinations thereof.
 32. A media sheet as in claim 22,wherein the unreacted additive or the undesired electrolytes are removedby a process selected from the group consisting of ultrafiltration,dialysis, ion exchange, reverse osmosis, and combination of processthereof.
 33. A media sheet as in claim 32, wherein the step of removingis by ultrafiltration.
 34. A media sheet as in claim 33, wherein theultrafiltration is carried out using a porous filter having an averagepore size from 20 nm to 100 nm.
 35. A media sheet as in claim 22,wherein the coating composition further includes an air fade additive.36. A media sheet as in claim 22, wherein the porous surface has a pHfrom about 4 to about 7.5.
 37. A media sheet as in claim 22, whereinsaid unreacted additive or undesired electrolytes is removed from theinitial amount prior to combining the metal or semi-metal oxideparticulates with the polymeric binder.
 38. A media sheet as in claim22, further including a second coating composition applied to thecoating composition, said second coating composition being substantiallydevoid of any water soluble coating formulation additive.
 39. A mediasheet as in claim 22, further including an inorganic porous mediaprecoat applied between the media substrate and the coating composition.40. A media sheet as in claim 22, wherein the water soluble coatingformulation additive enhances at least one of a coating preparationproperty, a coating application property, or a media performanceproperty of the media sheet.